PS Engineering
PMA7000BT Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-780-0204
Page 2-4
Rev. 1, July 2015
Refer to FAA Advisory Circular 43.13-2B for more information. Failure to use correct techniques may
result in improper operation, electrical noise or unit failure. Damage caused by improper installation will
void the PS Engineering warranty.
NOTE: PS Engineering can make a custom wiring harness for the intercom. Call 1-800-ICS-AERO or see
www.ps-engineering.com
for details.
2.5.1
Noise
Due to the variety and the high power of radio equipment often found in today's general aviation aircraft,
there is a potential for both radiated and conducted noise interference.
The PMA7000BT power supply is specifically designed to reduce conducted electrical noise on the aircraft
power bus by at least 50dB. Although this is a large amount of attenuation, it may not eliminate all noise,
particularly if the amplitude of noise is very high. There must be at least 13.8 VDC present at the bottom
connector, pin 20, of the PMA7000BT for the power supply to work in its designed regulation. Otherwise,
it cannot adequately attenuate power line noise. Shielding can reduce or prevent radiated noise (i.e., bea-
con, electric gyros, switching power supplies, etc.) However, installation combinations can occur where
interference is possible. The PMA7000BT was designed in a RFI hardened chassis and has internal Elec-
tromagnetic Interference (EMI) filters on all inputs and outputs.
Ground loop noise occurs when there are two or more ground paths for the same signal (i.e., airframe and
ground return wire). Large cyclic loads such as strobes, inverters, etc., can inject noise signals onto the air-
frame that are detected by the audio system. Follow the wiring diagram very carefully to help ensure a min-
imum of ground loop potential. Use only Mil-Spec shielded wires (MIL-C-275000, or better).Under no
circumstances combine a microphone and headphone wiring into the same shielded bundle. Always use a
2- or 3-conductor, shield wire as shown on the installation wiring diagram.
Radiated signals can be a factor when low level microphone signals are "bundled" with current carrying
power wires. Keep these cables physically separated. It is very important that you use insulated washers to
isolate the ground return path from the airframe to all headphone and microphone jacks.
Adding a high-performance audio control system, particularly in conjunction with high-performance active
noise canceling headsets, cannot improve on older avionics that were designed for cabin-speaker use. PS
Engineering makes no claim that the audio panel will provide a noise-free audio quality under all installa-
tion conditions, particularly with older avionics.
2.5.2
Power
The PMA7000BT-Series are compatible with both 14 and 28 Volt DC systems. A two (2) Amp circuit
breaker is required for 14 VDC installations, and a three (3) Amp breaker for 28 VDC aircraft. Power and
ground wires must be a twisted #18 AWG pair. Connect airframe power ground to J1 (bottom connector)
Pin Z only. No dropping resistors are required.
2.5.3
Communications Push-to-Talk
An important part of the installation is the PTT (Push-To-Talk) switches that allow the use of your aircraft
communications radio for transmissions. There are three typical configurations that can be used. Select the
configuration that best fits the installation.
Only the person who presses their PTT switch will be heard over the radio. If the pilot and copilot both use
the PTT, the only pilot position has access to the radio. The pilot position will have PTT control regardless
of the mic selector switch or copilot PTT when the PMA7000BT is in the
OFF
/E
MG
mode.
a)
PTT is built into both pilot and copilot yokes.
b)
PTT is in pilot yoke only. This configuration requires a modified external PTT switch plugged in-
to the copilot's microphone jack. . When the copilot's PTT is pressed, the intercom switches the
microphone audio from pilot to copilot mic.
c)
No built in PTT. This requires two built in PTTs to be installed, or modified external PTT switch-
es to be used. Modify external PTT as required.